1. Field of the Invention
The present invention relates to an image shake preventing apparatus and particularly concerns an image shake preventing apparatus which can prevent image shake on a camera caused by vibration.
2. Description of the Related Art
In the conventional image shake preventing apparatus (vibration isolator) for an image-taking optical system of a television camera, a correcting lens for isolating vibration is movably placed in a plane orthogonal to the optical axis, and when vibration is applied on the camera (the image-taking optical system of the camera), the correcting lens is moved by an actuator in a direction for canceling out the vibration so as to correct the image shake. Japanese Patent Application Publication No. 2001-142103 discloses that vibration applied on a camera is detected as, for example, a detection signal of a shake detecting sensor (such as an angular speed sensor and an acceleration sensor or the like), which is inputted to an arithmetic part (microcomputer) via a sensor amplifier, and digital arithmetic processing such as integration is then performed on the detection signal in the microcomputer to find a correction value (displacement position or the like of the correcting lens) for correcting image shake.
The shake detecting sensor, the sensor amplifier, and the digital arithmetic processing in the microcomputer respectively have frequency characteristics. For example, in the shake detecting sensor, a detection signal is delayed in phase as the frequency rises. The sensor amplifier hence includes a phase correction circuit for correcting the delay. However, even if the phase correction circuit is mounted, it is difficult to perform perfect correction over all frequencies. Conventionally, a set value of a predetermined parameter for changing the frequency characteristic of the phase correction circuit is set, for example, at a value permitting a phase to be effectively corrected in a range of about 1 to 10 Hz. The value is set so as to effectively correct image shake in a frequency range regarded as a frequency range of typical vibration, which is likely to occur in a number of image-taking environments. The frequency range where the phase is effectively corrected can be changed by changing the set value of the parameter.
Further, as to the digital arithmetic processing in the microcomputer, a frequency range for obtaining an effective arithmetic result is limited, and the frequency range can be also changed according to a change in the set value of the prescribed parameter used for the arithmetic processing. Conventionally, such a parameter of the digital arithmetic processing is set so as to effectively perform the arithmetic processing in the frequency range of 1 to 10 Hz.
However, even when the value of the parameter is set so as to effectively correct image shake in the frequency range of 1 to 10 Hz as in the case of prior art, exclusively for frequency ranges around thresholds in the range of 1 to 10 Hz (around 1 Hz or 10 Hz), it is possible to set a parameter value for making more effective correction. Therefore, the frequency ranges around the thresholds cannot be optimally set by the conventional setting of the parameter. If frequencies of vibration may widely range from 1 to 10 Hz, it is the most suitable to set a parameter which can effectively make correction over the range of 1 to 10 Hz. In contrast, when most frequencies of vibration are limited to frequencies around 1 Hz or 10 Hz, the above-described setting of the parameter cannot be the most suitable. Further, in some cases, vibration may occur with a lower frequency or a higher frequency than the frequency range of 1 to 10 Hz. In this case, it is not possible to properly prevent image shake.
Since the image-taking environment of a camera is unknown at the time of shipping a product, the tendency of vibration cannot be specified. However, when pictures are actually taken, the tendency of vibration can be somewhat predicted from the image-taking environment. For example, when a camera is set on a hard ground, vibration of a high-frequency range is more likely to occur. On the other hand, when a camera is set on a soft ground, vibration of a low-frequency range is more likely to occur. Moreover, also in the case where a camera is mounted on a vehicle or used for broadcast on a helicopter, the frequency of vibration can be somewhat limited. Meanwhile, even when the tendency of vibration cannot be predicted from the image-taking environment, the state of a taken image is observed while actually changing a parameter, so that an optimum parameter can be specified.
The present invention has been achieved in view of the above-described circumstances and has as its object the provision of an image shake preventing apparatus which can optimally correct image shake in accordance with an image-taking environment, that is, the frequency tendency of vibration occurring on the camera.
In order to attain the above-described object, the present invention is directed to an image shake preventing apparatus, comprising: an image shake correction value obtaining device which detects vibration occurring on an image-taking optical system and obtains a correction value for correcting image shake according to the detected vibration, wherein a frequency range of the vibration where the image shake is effectively corrected by using the obtained correction value depends upon a set value of a predetermined parameter; an image shake correcting device which corrects the image shake according to the correction value obtained by the image shake correction value obtaining device; and a parameter changing device which changes the set value of the parameter in the image shake correction value obtaining device.
Preferably, the parameter changing device sets one of an all-frequency set value, a low-frequency set value, and a high-frequency set value effectively correcting image shake on vibration of all frequencies, low frequencies, and high frequencies, respectively, in a predetermined frequency range as a set value of the parameter.
Preferably, the parameter changing device sets a set value corresponding to a mode selected by a mode setting device, as a set value of the parameter.
Preferably, the parameter is used in one of signal processing and arithmetic processing for obtaining the correction value, and is related to a frequency of vibration.
According to the present invention, the set value of the predetermined parameter related to a frequency can be changed so as to change a frequency range of vibration where image shake can be effectively corrected. Thus, it is possible to optimally correct image shake according to an image-taking environment and so on.